1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to audio encoding and decoding apparatuses and, and more particularly, to audio encoding and decoding capable of recovering a high-quality audio signal at a low bit rate.
2. Description of the Related Art
In related art audio encoding apparatuses, a time-frequency transform encoding scheme has been used. The time-frequency transform encoding scheme transforms an audio signal in a frequency space to obtain coefficients by using a modified discrete cosine transform (MDCT) and the obtained coefficients are encoded. However, the time-frequency transform encoding scheme has a problem in that quality of audio deteriorates at a low target bit rate.
As an example of a method of encoding an audio signal at a low bit rate, there is a parametric encoding method. In the parametric encoding method, sinusoidal waves are detected from the input audio signal, and frequencies, phases, and amplitudes of the sinusoidal waves are encoded. Specifically, it is possible to encode the input audio signal at a low bit rate in the parametric encoding method as it can have an effect of encoding many MDCT coefficients, even though it encodes by detecting a few sinusoidal waves having a large amplitude from the input audio signal.
However, in the parametric encoding method, in order to recover a high-quality audio signal, a large number of the sinusoidal waves need to be detected from the input audio signal. According to the parametric method, in a case where a frequency and amplitude of the input audio signal is constructed with a fixed sinusoidal wave, the audio signal can be sufficiently recovered by encoding one amplitude, one frequency, and one phase.
On the other hand, in a case where the frequency and amplitude of the input audio signal is constructed with a plurality of sinusoidal waves, in order to recover a high-quality audio signal, a large number of sinusoidal waves needs to be detected from the input audio signal, and the amplitudes, the frequencies, and the phases of the detected sinusoidal waves are encoded, so that encoding efficiencies deteriorate.
The parametric encoding method is suitable for a sinusoidal wave of which frequency is not changed according to time. However, since the frequency and the phase of the sinusoidal wave may be changed according to time due to noise or the like, the number of to-be-detected sinusoidal waves increases. Therefore, the parametric encoding method may be very inefficient.
That is, as the number of the detected sinusoidal waves increases, the number of the to-be-encoded amplitudes, frequencies, and phases increases, so that the parametric encoding method may be inefficient. Accordingly, the parametric encoding method is suitable for audio encoding and decoding apparatuses (i.e., audio codec) having a low target bit rate, but it is not suitable for audio encoding and decoding apparatuses having a high quality or a high target bit rate.